Add support for in-line generic patches to Flux Kustomization API

[glebiller]

The patchesJson6902 or patchesStrategicMerge fields in a Kustomize resource only allow patching single named resources. In order to patch multiple resources with a single patch, the generic patches field need to be used.

This PR implement the generic patches at the kustomize.toolkit.fluxcd.io/v1beta1/Kustomization level to unlock that feature.

One use case, would be for instance to override all path of all Kustomization at once without having to patch then one by one:

apiVersion: kustomize.toolkit.fluxcd.io/v1beta1
kind: Kustomization
metadata:
  name: podinfo
  namespace: flux-system
spec:
  # ...omitted for brevity
  patches:
    - patch: |-
        - op: replace
          path: /spec/path
          value: ./deploy/lab/
      target:
        group: kustomize.toolkit.fluxcd.io
        version: v1beta1
        kind: Kustomization

The field options from the original Kustomization is not implemented

  options:
    allowNameChange: true
    allowKindChange: true

This PR can only be merge if pkg PR #109 is accepted.

[glebiller]

Converted the PR to draft while waiting for pkg PR #109

[stefanprodan]

items must contain a target but in the blow example there is no target specified

[glebiller]

Thank you for the catch :)

In the original Kustomize resource, it's possible to apply a strategic merge patch (not JSON6902) without specifying the target.
I decided to force the target to be present in the Flux implementation for simplicity. Maybe that is something could be added in the future.

[stefanprodan]

One use case, would be for instance to override all path of all Kustomization at once without having to patch then one by one.

Having more than one Kustomization that points at the same path is not something you should ever do, as the controller will delete and recreate everything. Why are you doing this?

[stefanprodan]

@Kissy please update apis/kustomize to v0.2.0 in both go.mod files and then run make tidy.

[glebiller]

The use case I have in mind is:
each micro-services have their own git repository following that layout:

|- src & build files
|- deploy
    |- base
        |- Kustomization.yaml
        |- xxx.yaml
    |- test
        |- Kustomization.yaml
        |- patches.yaml
    |- prod 
        |- Kustmoization.yaml
        |- patches.yaml

Each git repository can be handled by a PR & permissions per teams with fine grain settings.
This layout follow the podinfo repository layout globally.

On the other side, the Infra team is managing a single repository with:

|- applications
    |- Kustomization.yaml
    |- app-1.yaml (1)
    |- app-2.yaml (2)
    |- ...
|- clusters
    |- test
        |- applications.yaml (3)
    |- prod
        |- applications.yaml (4)

(1) Would be a kustomize.toolkit.fluxcd.io/v1beta1/Kustomization source-ref to git repo of app-1
(2) Would be a kustomize.toolkit.fluxcd.io/v1beta1/Kustomization source-ref to git repo of app-2
(3) Would be creating a kustomize.toolkit.fluxcd.io/v1beta1/Kustomization with a patch targeting all kustomize.toolkit.fluxcd.io/v1beta1/Kustomization and overriding path to ./deploy/test
(4) Would be creating a kustomize.toolkit.fluxcd.io/v1beta1/Kustomization with a patch targeting all kustomize.toolkit.fluxcd.io/v1beta1/Kustomization and overriding path to ./deploy/prod

The Infra repo is clean and adding a new app / removing an app is done by adding or removing file in the applications folder.

[hiddeco]

I think this patch could be almost identically applied to the helm-controller which also has support for JSON6902 and strategic merge patches at the moment.

[stefanprodan]

@hiddeco I'm not sure it would work in all cases, as the patch can be on disk. While KC has the full source locally, HC doesn't. I don't expect people to place patches inside the chart, but for Git could work...

[stefanprodan]

each micro-services have their own git repository

Thanks @Kissy now I understand your use-case, the path is the same but the source is different so no conflicts 👌

[stefanprodan]

@Kissy apis/kustomize v0.2.0 contains the Patch field you've added to fluxcd/pkg.

[glebiller]

Successfully ran a test with an external cluster with:

    - patch: |-
        - op: add
          path: /metadata/labels/app.kubernetes.io~1instance
          value: podinfo-abcxzy
      target:
        labelSelector: app=podinfo

[stefanprodan]

LGTM

Thanks @Kissy 🏅